The back of a morbidly obese person; due to the person's rotund shape and cleavage created by fat on both the spine and shoulder blades. Similar to "back boobs"

Mary Jo spent 30 minutes hunting around the house for her keys when she heard her fat roommate jingling as she thudded by. She realized that her keys were lodged in her roomy's beetle back. (shudders and plucks them out)